Method:
1. Preheat oven to 180C.
2. Whisk together, flour and cocoa powder and set aside.
3. In a mixing bowl, whisk butter until creamy. To ensure that the recipe succeeds, the butter needs to be very soft.
4. Add in powder sugar and fleur de sel to butter and continue to whisk until light and creamy.
5. Whisk in egg white until it is well combined with butter cream.
6. Add in (2) and mix until well combined.
7. Spoon dough into a piping bag fitted with a star tip. Pipe dough into W shaped cookies.
8. Bake cookies at 180C for 10-12 mins - no more. The cookies will be delicate - transfer carefully into cookie jar after cooled.